self healing concrete

Self-healing concrete is also known as “BIO CONCRETE” Or “BACTERIAL CONCRETE”.

It heals itself when it comes in contact with air and water, it produces lime on the outer layer of the concrete.

In that CASE, the hydrated process may start again and hydration products may fill up and heal the cracks.

the width of range 0.05-0.1mm act as capillary and the water particles seep through the cracks. These water particles hydrate the non or partially reacted cement and the cement expands, which in turn fills the crack.

But when the cracks are of greater width, need of other remedial work is required. One possible technique is currently being investigated and developed was based on application of mineral producing bacteria in concrete.

Necessity

The American Concrete Institute as per ACI 302.1-04 addresses this issue, even the best construction & concreting cannot prevent cracking in concrete, and 0% cracks is an unrealistic thing.

REASONS WHY CONCRETE CRACKS

Concrete can withstand compressive forces very well but not tensile forces. When it is subjected to tension it starts to cracks, which is why it reinforced with steel to withstand the tensile forces.

•Concrete expands and shrinks due to temperature differences

•Due to the heavy load applied or

•Settlement of structure

•Due to corrosion of reinforcement steel

•Improper cover provided during concreting

•High water-cement ratio to make the concrete workable

bacteria use in self-healing CONCRETE

It contains an outer layer of a thick wall, which resist sunlight, chemical exposure etc.

mixing

      While preparation of concrete, this product is added in the wet concrete when the mixing is done

Preparation of bacterial concrete

Bacterial concrete can be prepared in two ways,

•By direct application

•By encapsulation in lightweight concrete

In the direct application method, bacterial spores and calcium lactate is added into concrete directly when mixing of concrete is done. The use of this bacteria and calcium lactate doesn’t change the normal properties of concrete.

The bacteria are exposed to climatic changes. When water comes in contact with this bacteria, they germinate(grow) and feed on calcium lactate and produces limestone. Thus sealing the cracks.

By encapsulation method, the bacteria and its food i.e. calcium lactate, are placed inside treated clay pellets and concrete is prepared. About 6% of the clay pellets are added for making bacterial concrete.

When concrete structures are made with bacterial concrete, when the crack occurs in the structure and clay pellets are broken and the bacteria germinate and eat down the calcium lactate and produce limestone, which hardens and thus sealing the crack. Minor cracks about 0.5mm width can be treated by using bacterial concrete.

Chemical Process of Self-Healing or Bacterial Concrete

Cao + H2O =  Ca(OH)2

Ca(OH)2 + CO2     =   CaCO3    + H2O

      When the water comes in contact with the unhydrated calcium in the concrete, calcium hydroxide is produced by the help of bacteria, which acts as a catalyst. This calcium hydroxide reacts with atmospheric carbon dioxide and forms limestone and water. This extra water molecule keeps the reaction going